A fourth Generation (4G) communication system, which is a next-generation communication system, is advancing to provide users with services of various Quality of Service (QoS) levels at a data rate of about 100 Mbps. In particular, researches are conducted on the 4 G communication system to support a high speed service by ensuring mobility and QoS in a Broadband Wireless Access (BWA) communication system such as wireless local area network system and wireless metropolitan area network system. As a solution for ensuring mobility of a terminal and flexibility of a wireless network configuration and for providing more efficient services in a wireless environment under severe change of traffic distribution or traffic requirement, the next-generation communication system is considering a communication system which adopts a multihop relay transmission using a relay station. By employing the relay station in the wireless communication system, coverage increase of a base station and throughput enhancement can be attained.
Two-hop communications between a Base Station (BS) and a Mobile Station (MS) via a Relay Station (RS) are shown in FIG. 1A. In FIG. 1A, the BS 110 and the MS 120 each intend to transmit data, and the RS 130 relays the transmit data of the BS 110 and the transmit data of the MS 120. More particularly, the BS 110 transmits 101 data D1 to the RS 130 and the RS 130 transmits 103 the data D1 to the MS 120. The MS 120 transmits 105 data D2 to the RS 130 and the RS 130 transmits 107 the data D2 to the BS 110. In the two-hop relay communication of FIG. 1A, the transmission and reception of four phases in total is required to deliver the data of the transmitter and the receiver. That is, four-time transmission time intervals are required to deliver the data of the transmitter and the receiver. To reduce the time taken for the relay communications; that is, to reduce the number of the transmissions and to thus raise the resource utilization, a three-phase bidirectional relaying method is suggested. The three-phase bidirectional relaying method is also called a Network Coding (NC) method.
Two-hop communications based on the three-phase bidirectional method are shown in FIG. 1B. In FIG. 1B, the BS 160 and the MS 170 each want to transmit data, and the RS 180 relays the transmit data of the BS 160 and the transmit data of the MS 170. More specifically, the BS 160 transmits 161 data D1 to the RS 180 and the MS 170 transmits 163 data D2 to the RS 180. The RS 180 applies exclusive OR (XOR) operation to the data D1 and the data D2 and transmits 165 data D1⊕D2. The BS 160 and the MS 170 receiving the data D1⊕D2 recover the transmit data of the sender by applying the XOR operation to their transmit data and the data D1⊕D2. By applying the three-phase bidirectional relay to the two-hop relay communication as shown in FIG. 1B, the data transmissions of the transmitter and the receiver are accomplished merely with the three-phase transmission and reception.
When the three-phase bidirectional relaying method is applied as discussed above, the capacity of the system is limited by the capacity of the poorer channel of the channel between the RS and the BS and the channel between the RS and the MS. In other words, even when the channel quality between the RS and the BS is quite good, the poor channel quality between the RS and the MS decreases the total capacity of the system. In this situation, most of the channel capacity between the RS and the BS becomes the redundant resource. In this regard, what is needed is a solution for enhancing the performance of the relay wireless communication system by efficiently utilizing the redundant resource.